This invention relates to a combined thin film magnetic head for magnetically reading and recording information on a magnetic recording medium. Such a combined thin film magnetic head is particularly useful in a magnetic disc unit.
Such a combined thin film magnetic head comprises a reading part and a recording part which are formed through a first insulator layer on a non-magnetic substrate to overlap each other. The reading part is for magnetically reading information on a magnetic recording medium with reading sensitivity. The recording part is for magnetically recording the information on the magnetic recording medium. The non-magnetic substrate has a main surface for forming the reading part and the recording part and a substrate side end defining an air bearing surface for the magnetic recording medium. The reading part comprises an under shield layer formed on the first insulator layer, an upper shield layer covering the under shield layer, and an MR (magneto-resistive) element formed between the under and the upper shield layers through a second insulator layer. The magneto-resistive element is for magnetically reproducing the information on the magnetic recording medium and produces a reproduced output voltage. For this purpose, the magneto-resistive element is supplied with a sense current as known in the art. The recording part is formed over the reading part.
Each of the under and the upper shield layers is generally made of a permalloy film and has a shield area substantially equal, in size, to the main surface of the non-magnetic substrate. The magneto-resistive element has an element pattern which is much smaller than the shield area. The magneto-resistive element is connected to first and second element terminals through first and second wiring patterns both of which are formed between the under and the upper shield layers through the second insulator layer. The first and the second wiring patterns are made of non-magnetic metal material to flow the sense current. In such a combined thin film magnetic head, it is possible to independently optimize recording characteristic and reproducing characteristic. Furthermore, if a recording width is wider than a reproducing width, it is possible to increase a read margin on off-tracking. Such a combined thin film magnetic head is generally called a wide write/narrow read type or an MR/inductive combined thin film magnetic head and can improve performance of a magnetic disc unit.
It should be noted here that a space between the magneto-resistive element and the under shield layer is, generally, within the bounds of 0.1 through 0.5 micron meters. The space between the first and the second wiring patterns and the under shield layer is equal to the above-mentioned value. This applies to the space between the magneto-resistive element and the upper shield layer and the space between the first and the second wiring patterns and the upper shield layer. In other words, the second insulator layer between the first and the second wiring patterns and the under shield layer is very thin. This applies to the second insulator layer between the first and the second wiring patterns and the upper shield layer. In this event, defects, such as a pin hole, often occur in the second insulator layer. In other words, a short circuit is formed between the first and the second wiring patterns and the upper or the under shield layer. The short circuit causes a shunt current of the sense current flowing the first and the second wiring patterns. The shunt current causes not only degradation of the reading sensitivity but also occurrence of signal noises.